[PATCH v3 06/13] lib/crypto: sm3: Provide a function for zeroizing the sm3_ctx structure

[Thomas Huth]

In certain cases crypto code functions need to zeroize their local
sm3_ctx structure after use to avoid leaking sensitive material. Provide
a sm3_zeroize_ctx() helper function that e.g. can be used with __cleanup()
to automatically zeroize the structure when it goes out of scope.

While we're at it, replace the related memzero_explicit() call in
lib/crypto/sm3.c with a call to the new helper function.

Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx>
---
 include/crypto/sm3.h | 10 ++++++++++
 lib/crypto/sm3.c     |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/crypto/sm3.h b/include/crypto/sm3.h
index 371e8a6617054..d044ca80213ba 100644
--- a/include/crypto/sm3.h
+++ b/include/crypto/sm3.h
@@ -11,6 +11,7 @@
 #define _CRYPTO_SM3_H
 
 #include <linux/types.h>
+#include <linux/string.h>
 
 #define SM3_DIGEST_SIZE	32
 #define SM3_BLOCK_SIZE	64
@@ -41,6 +42,15 @@ struct sm3_ctx {
 	u8 buf[SM3_BLOCK_SIZE] __aligned(__alignof__(__be64));
 };
 
+/**
+ * sm3_zeroize_ctx() - Zeroize an sm3_ctx structure
+ * @ctx: The sm3_ctx to zeroize
+ */
+static inline void sm3_zeroize_ctx(struct sm3_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 /**
  * sm3_init() - Initialize an SM3 context for a new message
  * @ctx: the context to initialize
diff --git a/lib/crypto/sm3.c b/lib/crypto/sm3.c
index b02b8a247adf2..23059347b4493 100644
--- a/lib/crypto/sm3.c
+++ b/lib/crypto/sm3.c
@@ -258,7 +258,7 @@ static void __sm3_final(struct sm3_ctx *ctx, u8 out[SM3_DIGEST_SIZE])
 void sm3_final(struct sm3_ctx *ctx, u8 out[SM3_DIGEST_SIZE])
 {
 	__sm3_final(ctx, out);
-	memzero_explicit(ctx, sizeof(*ctx));
+	sm3_zeroize_ctx(ctx);
 }
 EXPORT_SYMBOL_GPL(sm3_final);
 
-- 
2.55.0